Machinery and equipment that are used at many production sites are, typically, controlled by a control system that is constituted by a programmable logic controller (hereinafter, also referred to as “PLC”) or the like. Such a control system collects field information from external switches, sensors and the like, and outputs instruction values obtained by computations that are based on the collected information, in order to perform predetermined control on machinery and equipment.
Such collection of field information and output of instruction values are often performed via a network. For example, JP 2012-194631A discloses a network system formed by at least one or more master devices and a plurality of slave devices being connected via a network.
JP 2012-194631A is an example of background art.
There are systems that are configured such that, in the case of newly adding a slave device to the topology of a network such as described above, the setting value of a node address is automatically written to the added slave device, based on the position of the slave device in the topology. In such systems, when processing in which the setting value of the node address is written is performed, there are cases where the setting value of the node address is written to an unintended slave device when a change occurs in the topology. In such cases, the setting value of the node address of a slave device that was operating normally till then will be rewritten, thus causing problems such as an anomaly in the network or a malfunction of the slave device caused by the setting value of the wrong node address.
Also, in the case where such an anomaly or malfunction occurs, it takes time to restore the system, since tasks such as specifying and resetting the slave device that was mistakenly rewritten are necessary, even when it is known that the setting value of the node address was mistakenly rewritten.
One or more aspects have been made in order to solve the abovementioned problems, and an object thereof is to provide a communication system, a communication device and a communication program that enable an address of a slave device to be efficiently configured to a correct state.